1. Field
This invention relates to the field of antenna arrays, and more specifically, to a high-gain antenna array in which the beam direction can be steered without the use of classical phase shifters and beamformer circuitry.
2. Background
An antenna is a device that indiscriminately broadcasts a signal in every direction and in a pattern referred as a “radiating signal pattern.” The direction of a signal sent by a single antenna cannot be controlled. Antenna arrays are groupings of antennas that control the direction of a signal by enhancing the signal in a desired direction while diminishing the signal in non-desired directions. Signals transmitted along such a directional path are referred to as “beams”.
Beam control is important for coordinating communications. Antennas may be used to communicate between one or more moving stations, such as ships, aircraft, satellites and ground stations. Communication with moving objects requires that the beam path be continuously and precisely adjusted, or the object will lose communication. Precise beam control may also be necessary to prevent a signal from being intercepted.
Antennas in arrays are passive devices through which a beam can be mechanically or electronically steered. Antennas are mechanically steered by strategic positioning or by geometric alterations. Antennas are electronically steered by altering the transmission signal fed into them. Electronic steering varies the phase and amplitude of the electronic signal fed into each antenna of the array. This type of array is referred to as a “phased antenna array”.
A major component of the phased antenna array is the feed assembly component. The feed assembly receives the incoming radiofrequency (RF) signal for the entire array and splits it between multiple signal-altering components. Signal-altering components include phase shifters, amplifiers and attenuators. Amplifiers increase signal strength and attenuators reduce it. The beam direction for each composite phased antenna array is a result of the output signals emitted by each antenna in the array.
Phase shifter components direct the signal down multiple circuit paths of different lengths within the phased antenna array. A switching controller determines which path the signal goes down by opening and closing multiple switches for each path. The different paths delay the signal by varying amounts, altering the phase. The greater the number of paths at varying lengths, the more precise the switching capability.
One problem with conventional phase shifters known in the art is a limitation on the number and length of lines it is practical to put into a phase shifter. Increasing the number of lines requires complex circuitry and processing capability, adding to cost and energy requirements. Increasing the number of switches between the input and output lines increases the likelihood of component failure.
Another problem known in the art is referred to as “beam squint.” Beam squint refers to the problem of maintaining a consistent beam position over a wide range of frequencies without introducing error inherent in digital phase shifting.
A significant cause of beam squint is that classical phase shifters must approximate the path for steering a beam in modulo 2π phase mode. The modulo 2π approximation range is a limitation on accurate approximation. This error is introduced at high and low frequencies. With conventional phase shifters, errors may be produced during phase shift of up to 360/2n degrees, where n is the number of path lengths within the phase shifter. A conventional phase shifter with four paths may introduce a phase angle error of up to 22.5 degrees. Phase errors can increase the amount of power wasted, and angle errors can lead to unacceptably poor broadband performance.
There is an unmet need for a phased antenna array that provides more precise beam steering capability, that has failure-resistant components, and that is less prone to beam squint error.